I am sorry to hear your plight.
Do you have a guarantor?
I would advise legal council.
Are you a member of the NRLA?
In such situations you need a deed of surrender to protect yourself (Tenant asking for tenancy end)
You certainly don’t want to refund a deposit whilst she is in situ
It’s the only thing left that you can bargain your deed of surrender with even if the deposit is in a custodial scheme
There is a legislation but I don’t know if you can enforce it because she’s refusing rent payment and I don’t know if there is a guarantor in place Ancient law may help landlords - The Landlord Law Blog
Can you negotiate with the deposit or have you already released it on the website?